This invention relates generally to gas burners and more particularly to gas burners used as surface heating units in cooking appliances and apparatus and methods for improving operation of such burners.
For gas burners used as surface heating units in cooking appliances such as ranges and cooktops, a high turndown ratio, which is a ratio of maximum output to minimum output, is often desirable. For a given burner, the maximum output typically signifies the “power” or “speed” of the burner and the minimum output is related to the simmer capability of a burner. The maximum output is limited by system gas flow handling capabilities and safety considerations. The minimum output is limited by the ability of the burner to maintain a stable flame under transient pressure fluctuation conditions such as may be caused by air currents in the room, or sudden opening or closing of under the cooktop's cabinet doors or oven door.
Either horizontal or vertical staging of cooktop burners is used for improving cooking performances. A horizontally staged burner uses two or more rings of gas outlets or ports that are staged radially in a somewhat horizontal plane. The inner most stage is often used for simmer while all the combined stages are used for power cooking. In a vertically staged burner, either of two stages can be used for simmer while the combination of both stages is utilized for power cooking. In a vertically staged burner, if the simmer stage is the lower of two stages then this configuration has the added advantage of distance between the flame and a pot placed on top of the cooktop burner. Nevertheless, the above limitations on performance also apply to the horizontally and vertically staged burners.
A vast majority of gas burners used in cooking applications are partially pre-mixed burners using both primary-air and secondary-air. Based on whether the primary-air is drawn from above the cooktop or below the cooktop, these burners are either top-breathers or down-breathers respectively. Top-breather burners sometimes referred to as open or non-sealed burners, are insensitive to pressure fluctuations due to oven or cabinet doors but are sensitive to room air currents. The turndown of these burners is also limited due to lower port loading design constraints. In down-breather burners, also referred to as sealed burners, there is no gap around the burner to allow spills or air to get inside the cooktop. The sealed burners are sensitive to pressure fluctuations under the cooktop.
The partially-premixed burners generally use a venturi to induce primary-air into the burner and mix it with the fuel gas ejecting from the gas orifices. Venturi design has been traditionally mostly empirical or experimental. A burner designer looks at the physical geometrical constraints and then uses scaling factors or past experience to design the venturi. Optimization is also by trial-and-error. This does not fully exploit the potential of the venturi and slows down the design process and compromises performance of the partially-premixed burners.